Chronographic apparatus and method



H. w. HOFFMAN ETAL CHRONOGRAPHIC APPARATUS AND METHOD sept, 2o, 194,9.

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w. HOFFMAN STAI. 2,482,184 CHRONOGRAPHIC APBARATUSAND METHOD Sept.v zo,1949.-

Filed may 26,f 1945 f @Rove H. HELMER.

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Sept.20, 1949. H. w. HOFFMANl ETAL 2,482,184

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CHRONOGRAPHIC APPARATUS AND METHOD 8 Sheets-Sheet 6 Filed lay 26, 1945 YGROV R H.HE MER. om

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CHRONOGRAPHIC APPARATUS AND METHOD 8 Sheets-Sheet 7' Filed lay 26, 1945Sept. 20, 1949. H. w. HOFFMAN ErAl. v 2,4825184 CHROOGRAPHIC APPARATUSAND METHOD Findlay 26, 1945 a sheets-snm a FES." 15 Figf 16 Ramal:Dsuncron INVENTORSI HARRY \l-/. HOFFMAN. @ROVER H. HELMER.

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Patented Sept. 2o, 1949 CHRONDGBAPHIC generos AND METH() William Henman,Anoka, and Grover H..-

Helmer, St. Louis Park, Minna,

assignora to Federal Cartridge Corporation, Minneapolis, Minn., acorporation of Minnesota y appuesaoamy ze, 1945, sesame. secon s cum.(ci. isi-15) This invention relates to improved chronosraphic apparatusand methods and more particularly to apparatus and methods for timingevents at exceedingly short intervals. The apparatus and methods of theinvention are of. narticular usefulness in measuring and recording theperformance of ordnance projectiles and isV hereinafter speciilcallydescribed with reference to such work, although it must be understoodthat such speciilc application is merely illustrative.

It is an object oi the invention to provide improved chronographicapparatus and methods and particularly to provide apparatus and methodsfor accurately indicating and recording time intervals of exceedinglyshort duration and utilizing photoelectric pick-up apparatus. It is alsoan object ofthe invention to provide apparatus and methods oi indicatingand recording the performance of ordnance projectiles and other rapidlymoving objects. Another object is to provide improved circuit apparatusand methods, and sensitive photocell pick-up devices.

Other and further objects are those inherent in the apparatushereinafter illustrated, described and claimed. l

The invention is illustrated with reference to the drawings in whichteFigure 1 is a schematic plan view of the sys- Figures 2 and 3 are,respectively, front and side elevational views of a light source withits power supply and standard that is used in the system in conjunctionwith a photocell apparatus, illustrated in Figures and 6;

Figure 4 is an enlarged detail of the photoeleetric cell support;

Figures 5 and 6 show, respectively, front and sideelevational views ofthe sensitive photocell pick-up, self-contained amplifier and powersupply and standard therefor;

Figure 7 is a wiring diagram of the light source and power supplytherefor;

Figure 8 is the wiring diagram of the photocell and its associatedamplifier;

Figure 9 is the wiring diagram of the power supply and output triggertube apparatus of the photocell pick-up;

Figures 10 and 11 are, respectively, front and side elevational views ofthe indicating and recording instrument;

Figure l2 being a fragmentary vertical sectional view of a part of thisapparatus taken along the line I2-I2 of Figure 10;

Figures 13 and 14, taken together, show the wiring diagram of theindicating and recording ss instrument, and the ,ampliera power supply.switching and testing apparatus therefor. Figure 13 should be placed atthe left and 4Figure 14 at the right so as to show the complete diagram:

Figures 15 and -16 are, respectively, front and side, elevational viewsof the amplifiers, power supply, switching and testing apparatus; and

Figures 17, 18 and 19 are diagrammatic views showing, respectively, theRead," Range" and Disjuncture" operating condition switches I-X of thestation unit.

Throughout the drawings corresponding numerals refer to the same parts.

General arrangement, Figure 1 Referring to the drawings, Figure 1 showsa schematic plan view of an illustrative installation. in this casespeciiically an ordnance test nring range. The ordnance piece.undergoing-testing is shown at Il,`and may, for example, be a smallarms riiie such as a 30 caliber or 50 caliber machine gun or a largerpiece. 'Ihe rifle, if such be the ordnance piece undergoing testing. ismounted in nxed position and ilres down the range, along line I I-I Iinto a sandbag or other suitable bunker I2. Along the line of projectileflight there are two spaced pick-up stations, namely the muzzle stationvI3 and the range station I4. `AI: the muzzle station there is a lightsource unit I I and a photocell and amplifier unit I8, and at the rangestation an identical light source unit 20 and identical photocell andampliiler unit 22. The photocell units I8 and 22 and the light sourceunits I8 and 20 are supplied with power by alternating current supplylines designated L1 and La. The output (signal) from thephotocell-amplier I8 and muzzle station I3 is transmitted to the stationunit 25 by means of a pair of signal lines K and G, line G beinggrounded as indicated at 26. Similarly the output (signal) of thephotocell-amplifier unit 22 is transmitted to the station unit 25 bymeans of lines N and G', the latter being grounded at 21. The variousunits and their mode of interconnection and operation will be describedin greater detail hereinafter.

Light source units 16 and 20, Figures 2, 3 and 7 The range and muzzlestation light source units I6 and 20 are identical and are illustratedin Figures 2, 3 and '7. These units are made movable and include a basegenerally designated 30 to which is welded an upright standard generallydesignated 3|. Base 30 cousistsof a housing 32 adequately braced andprovided with a iloor 25. The housing is preferably open at one side toreassai ceive a steel case 3l housing the power source o! the light, ashereinafter described. Case 80 is preferably made of strong metal. heavywalled. and may have a Ventilating grill 81 if heat losses are notadequately dissipated by radiation.

The upright standard is conveniently a simple steel channel 38 ofU-shaped cross section having a pair of webs 8s and 4l weldedthereacross to support the sockets 4| and 42 of the lumiline type lamp43. A pair of conductors 44-40 are draped in the channel and are thusprotected, the conductors extending down into the power supply case l.

`terminal of the primary winding 48 of transformer 50, and is alsoconnected through lino 52 to the anode or anodes 53 of the rectifiertube 54. Line La is connected to the other terminal of winding 49 andthence through .iuctions l5, 88 and line 45 to the lumiline lamp 48,whence the circuit continues through line 44, to junction 51 and thencethrough iron cored reactor 8| and junction 58 to terminal 08 of thesecondary 5| of the transformer. The filament (cathode) 65 of tube 54 isconnected directly across the secondary winding 5|. Capacitors I8 and 80are connected across the direct current output lines on either side oithe reactor 6|, as shown. In operation the transformer 50, rectifier I4and the lter composed of capacitors 59 and 00 taken with reactor 6iserve to supply smooth direct current at appropriate voltage acrosslines 44 and 45, thus energizing lamp 48 so as to produce a uniformdegree of illumination. Flashing oi the light or stroboscopic effectswhen lamps are energized from an alternating current line are therebyavoided. This is important in the very sensitive photoelectricapplication here illustrated.

The photocell units 8 and 22 occupy positions directly across from theircooperating light sources i6 and 20, respectively, as shown in Figure 1and are positioned so as to intercept light from the lamp 43 of thelight unit. Photocell unit i8 is arranged to intercept light projectedin the direction of line 101|, while photocell unit 22 intercepts lightin the direction of line 18-14. The lines of light 10-1I and 13-14 areacross the path of night of the projectile, hence the movement of aprojectile from the piece l0 towards f bunker I2 causes an instantaneousdecrease in light falling on photocell |8 and a short interval later,depending upon distance D, Figure Land the velocity of the projectile, asimilar instantaneous decrease occurs at photocell 22.

The time duration of these periods of decreased light intensity and thepercentage variation in light intensity are both exceedingly small.Hence, a high degree of sensitivity and rapidity of response arerequisite freedom from interference and accurate signal transmission. Toaccomplish these purposes there are provided the photocell, amplier andpower supply units |8 and 22.

Photocell, amplifier and power supply units 18 and 22, Figures 5, 6, 9and 10 For the purposes of the specifically illustrated embodiment ofthe invention. viz. ordnance testing, the photocell units I8 and 22 maybe identical; hence only one need be described.

The combined photocell, amplifier and power supply unit I8 or 22includes a base 15 and standard 18 of construction and dimensionssimilar to that yillustrated for the light source. The base 'il includesa housing 18 stiened with angle iron which may be open at one side toreceive the power supply case 82, which is made of stout sheet metal andprovided with grill Il. The case rests on the welded in door I5. Post 16is of square or round hollow steel tubing, terminating in a boxlikeampliiier case 81 which has a front cover Il removably attached thereto.On top of the amplitler case 81 there is mounted a smaller steel cupola80. An opening 85 from the top of the ampliiler case into the cupola isprovided so as to allow the photocell which is mounted on the amplinerto be inserted. The cupola 80 has a light aperture 83, behind which ispositioned the photocell. Case 8| forms a complete shield for thephotocell, which is exposed to light only through window 88. Wiring fromthe power supply case 82 to the amplier case passes through the hollowpost 'Ii and the support and wiring between the ampliiier and photocellpasses through the small interior opening. not illustrated, betweenthese cases. Each unit is thus completely shielded electrically and isso ruggedly mounted that sound and other mechanical vibrations produceno deleterious effects in the circuits. The light source units I5 and 20and the photocell units |8 and 22 are painted black inside and out.

Figure 8 is a wiring diagram of the photocell and amplifier chassiswhich is mounted in case 88 and cupola 90. This unit includes a base 00which physically supports two heavy walled boxes I0! and |02 which servein turn as electrical shields and cases for the several amplifierstages. Boxes |0| and |02 are supported on sponge rubber pads |03 and|08 so as to damp out mechanical vibrations. Base |00 serves also tomount a connection socket |04 having terminals I through 8 which serveto connect the amplifier-photocell instrument, Figure 8, to the powerpack and thyratron trigger tube unit, Figure 9. These terminals have thefollowing purposes: Terminals and 8 supply illament current for thethrce amplifier tubes of Figure 8. Terminals 2, 4 and 6 are connectedtogether and to ground through ground lines hereinafter traced. Terminal3 supplies high voltage direct current (in this illustration,speciilcally 380 v. D. CJ. Terminal 1 supplies an intermediate directcurrent voltage (in this illustration, specically v. D. C.). Terminal 5carries the signal output of the amplifler, Figure 8. to the gas-filledtrigger tube (thyratron) in the unit, Figure 9.

The entire unit composed of base |00, shield boxes |0| and |02 andphotocell |05 is housed in the box 81 and photocell cupola 80. Box 90may be provided with an extra ground via line |08 to ground |01.

From the top of shield |0| there extend two copper tubes ||0 and whichare positioned on shield |0| so that they will reach through port box 81into the photocell cupola 80 when the chassis |00 is in place in theunit. Conduits ||0 and serve to support the photocell |05 and also serveas electrical shields for conductors |29 and |35 extending down from thephotocell into the ampliiler. As shown in Figure 4, the conduits ||0 andare provided at their lower ends with female gland nuts H0 and III'which soldered to the center post ||3 oi socket ||1.

Lead wires |20 and |00 extend from terminals |20a and |00a (at the lowerends of conduits III and III) through the conduits and thence toterminals |20' and |30' on the socket. The photoelectric cell |05 issimply plugged into the socket ||1 when servicing or renewal is desired.It may be noted that conduits and extend up closely to socket terminals|20' and |00' but do not touch them, thus providing shielding as well asmechanical support to a position close to the socket, the mechanicalsupport being then carried through post ||3.

` From the intermediate voltage direct current supply terminal 1, plug|04, line ||4 extends through resistor to terminalV ||0 whence thecircuit continues along ground line ||0 through junction ||0|20. Abranch of line ||0 extends to junction |21 which groundsline ||0 to case|0| and thence to ground terminals 2, 4 and 0 on plug |04. From variablepositive tap |20 line |20 extends through junction |30 and through theconduit ||0 to the anode |00 oi the photocell |05. The circuit extendsfrom the cathode |34 of the photocell through line |30 to junction |01and thence through capacitor |30 to junction |30 which is connected byline |40 to control grid |43 of the pentode amplier tube generallydesignated |4|.

The tube |4| has a cathode |42 indirectly heated by lament |41, controlgrid |40, a second grid |44, a screen grid |45 and a plate |40. Fromjunction |30 on line |40 a circuit extends through resistor |40 tojunction |40 and thence to the negative terminal oi a bias cell |50. Thecircuit extends from the positive terminal oi' the bias cell |50 throughresistor |5| to junction VI|0 on the ground line |0. A condenser |53 isconnected from the negative terminal |40 of the bias cell to junction|20 on the ground line 0. From junction |01 a circuit extends throughresistor |2|. thence through junction |3| to ground terminal H0. Acondenser |32 is connected across terminals |00 and |3|, thus bridgingthe 'major part of resistor ||5.

From junction |2| on the ground line a circuit extends through line |54to cathode terminal |55 and thence to the cathode |42 of ampliiier |4I.The screen grid |45 is connected to the cathode terminal |55. The secondgrid |44 is connected through line |51 to junction |50 and thencethrough resistor |50 to junction |00, from which the circuit extendsthrough line |6| and condenser |62 to junction |24 on the ground lineH0. From junction |50 on the lead |51 oi' grid |44, a circuit extendsthrough line |00 to junction |54 and thence through a continuation oiline |03 and condenser |05 to junction |22 on the ground line ||0. 'Tojunction |04 therev is connected a resistor |01, the opposite terminalof which is connected to junction |23 on the ground line |0. The plate|40 of the ampliiler tube |4| is connected through line |00 to junction|10 and thence through condenser |1| and through resistor |12 tojunction |20 on the ground line ||0. A circuit extends from junction |10through resistor |13 to junction |14 and thence through resistor |15 andline |10 to the high voltage terminal 3 of the connection socket |04.Junction |14 is connected through line |10 to junction |00.

Amplifier tubes generally designated |00 and Y 8 220 are housed in thesheet metal box |02. Ampliner tube |00 has a cathode |0| indirectlyheated by illament |01, a control grid |02, a second grid |03 and ascreen grid |04 and plate |00. The control grid |02 is connected throughline |00 which is shielded throughout its length by means of shield |00.The line |00 extends to a variable tap |00 on the resistor |12 of theilrst l stage of amplification. The cathode |0| is connected throughline |0| to terminal |02 and thence through the resistor |00 to terminal|05 on the ground line |04. The ground line |04 is grounded at |00 uponthe metal case |02, the line |04 being extended to terminal 0 of theconnector socket |04. From junction |02 a circuit extends throughcondenser 202 to junction |01 on the ground line |04. The second grid 00and screen grid |04 are connected together externally and are connectedthrough line 204 to Junction 205 on the plate lead 200. The plate lead200 extends through junctions 205 and 201 and through condenser 200 andthence through line 4 200 and resistor 2|0 to Junction |00 on the groundline |04. From junction 201 on the plate lead a circuit extends throughresistor 2|| to junction 2|2 and resistor 2|3 to junction 2|4 on the(high voltage) supply line 2|5 which is connected to junction |11 online |10. A condenser 2 I0 is connected across junctions 2 |2 and groundterminal |00.

The third stage of ampliilcation is represented by amplifier tube 220which has cathode 22| indirectly heated from iilament 222, a. grid 223and plate 224. The grid 220 is connected to junction 225 on line 200,the cathode 22| being connected through line 221, junction 220, resistor220 to terminal 200 on ground lead |04. A condenser 230 is connectedaround resistor 220 from junction 220 to ground terminal 20|. The platecircuit of tube 220 extends from plate 224 through line 23|, junction232 and thence through resistor 234 to junction 235 and resistor 230 tohigh voltage supply via line 2|5. A condenser 230 is connected fromjunction 235 to ground terminal 20|. The output circuit of amplifiertube 220 is through condenser 240 and line 24| to terminal 5 on thesocket |04.

Referring to Figure 0 there is illustrated the combined wiring diagramof the gas-filled trigger tube and the power supply chassis. The powersupply serves not only that trigger tube 204 but also the amplifier andphotocell circuits of Figure 8. The entire apparatus of Figure 9 ismounted on a suitable base and is housed within the box 02 on the baseof the unit, Figures 5-6.

The incoming circuits to the unit of Figure 9 include an alternatingcurrent power supply lines L1 and Le which connects to a socket 242 ofsuch construction that there can be no reversal of these leads since oneof the leads (L1) is grounded. From terminal (line L1) 243, line 244extends to primary winding 245 oi' transformer 245, from which thecircuit continues through line 241, fuse 240, switch 240 to terminal 250and line L1. 'I'he transformer has a lament winding 252, the center tapbeing connected by line 250 to housing ground 254. The outside terminalsof winding 252 are connected by lines 255 and 255 to terminals l and 0,respectively, of the plug |04A which matches socket |04 of drawingFigure 8. Transformer 240 is provided with a plate voltage winding 251and a filament voltage winding 20| which are connected to rectifier tube202 in the customary manner as follows:

Winding 251 is connected to the two plates of the rectier and winding26| to filament 263. The rectiiier negative output line 265 b connectedto the midpoint 253 of transformer winding 251 and extends to thenegative terminal 261 of the potentiometer resistor 269. 'I'he positiveline of the rectier 262 extends from the filament secondary winding 26|through line 266 and extends through a choke coil 210 to the positiveterminal 21| of the potentiometer resistor. A pair of condensers 212 and213 are connected across the lines 265 and 266 and the chokes serve tosmooth out the rectined direct current output.

The potentiometer resistor 269 is provided with tap 214 which isconnected to the housing ground 254. The negative line 265 is, in thespecific device here illustrated, approximately 40 volts negative. Theresistor is also provided with a variable tap 215 of approximately 90volts, a variable tap 216 of approximately 180 volts and a high voltagetap 211 of approximately 380 volts. Tap 215 is connected by line 290 toterminal 1 on the plug |04A and the high voltage tap 211 is connected byline 28| to terminal 3 of the plug. Terminals 2, 4 and 6 of the plug areoonnected together and are connected by line 262 to the grounded tap 214of the potentiometer re- SiStOr.

A gas type trigger tube generally designated 234, having cathode 235,cathode heater lament 236, grid 231 and plate 268 is connected so as tobe controlled by the incoming signals on terminal 5 of plug |04A.Terminal 5 is connected by line 230 to junction 29| and thence throughresistor 232, switch 293, junction 294 to the control grid 261 of thetube. The cathode 235 of the tube is connected through resistor 296 tojunction 291 on the ground line, resistor 296 being paralleled by thecondenser 299. The resistor 296 is also arranged in parallel with a neonindicator light 300 which is connected through switch 30|. From tap 216on the potentiometer resistor line 333 extends through resistor 304 tojunction 305 on the plate circuit 306 of the trigger tube and thecircuit continues over line 301. through condenser 303 and thencethrough junction 309 and resistor 3| 0 tojunction 3| on the ground line232. Junction 309 serves as the output terminal and is connected by line3|3 to the output terminal 3|4 on the output plug generally designated3|5. A plug connection to socket 3|5 carries a ground line and a signalline. These are the pairs G and K or G' and N of Figure 1. Terminal 3| 6of the output plug is therefore grounded at the station unit 25 andhence line 3|1 extending from socket 3|5, Figure 9, serves as a groundfor that unit andalso for the parts shown in Figure 8 since these areal1 in the standard illustrated in Figures 5 and 6. Line 311, Figure 9,extends to junction 3|3 on the central tap lead 253 of the filamentsupply transformer, and thence through line 253 to junction 320 on thehousing ground line 254. From junction 294 on the grid line of thetrigger tube a circuit extends through resistor 322 to junction 323 onthe ground line and from junction 29| of the grid resistor 292 a circuitextends through resistor 324 to a variable tap 325 on resistor 326.Resistor 326 is connected to junction 321 on ground line 202 and isconnected through line 323 to the negative terminal 261 of thepotentiometer resistor. A condenser is connected between junction 321 onthe ground line and junction 330 on line 280.

Station apparatus The station unit 25 includes the apparatus 8 shown inFigures 10-12 and also the apparatus shown in Figures 13-16.

Figures 10, 11 and 12.*-Referring to Figures 10, l1 and 12 there isillustrated a unit having a base generally designated 335 on which ismounted a synchronous motor 336 which is coupled at 331 to the shaft333, the latter being supported in a pair of bearings 339 and 343,Figures 11 and l2. To the front of the base 335 there is fastened avertically positioned disk 342 which is attached in place by a pluralityoi? cap screws 343. The disk 342 serves as a mounting for the bearing343, Figure 12, and on the front end oi' the shaft 333 there is mounteda rotating unit generally designated 345. The unit 345 is ofnon-magnetic material and in its periphery is a groove which receives avery thin ring 341 of magnetic material which is fastened in place byany suitable means. 'I'he ring 341 of magnetic material serves to haveimpressed upon it the timing impulses.

On the front of the disk 345 there is mounted a dish-shaped cover 343which serves to mount a neon lamp 349 on the inside which ls visiblethrough a small aperture 350. The cover ls grooved at 352 and the grooveis painted black so as to correspond with the black inside 353 of thehousing in which the neon lamp is situated. One terminal of the neonlamp is grounded and the other terminal is carried out through lead 355to a central stud 355 against which the spring contact 351 presses.Contact 351 is mounted upon an upright member 353 of clear plastic orany other suitable material so that the flash of the neon lamp will bevisible through it. An incoming lead wire D is connected to the terminal351 so as to conduct the incoming signal wave to the neon lamp.

The disk 342 is provided with a bushing 36| which serves as a hub forthe adjustable radial arm generally designated 36| which extends outbeyond the edge of the disk. The disk is provided with an arcuate groove363 which extends about half way around the disk and through the groovethere extends a stud 365 which passes through member 36| and serves as asupport for another shorter member 366 that lies parallel to but be- Ihind the member 36|. Another arcuate slot 364 may be provided if desiredso as to allow a fastening rivet 363 to pass through the disk. Rivet 369serves with 365 to fasten member 366 in spaced parallel relation withthe outer part of radial arm 36|.

Between the protruding end 361 of arm 35| and 366 of arm 366 there ispositioned a rubber roller 310 which is mounted on a shaft 312 held inplace by a collar 313. On the front end of the shaft there is provided amanually adjustable knob 315. The location of shaft 312 is such that therubber roller 310 presses against the edge 342A of the disk 342 andhence as the knob 315 is rotated, this causes the roller 31| to grip theperiphery 342A and the members 36| and 366, as a unit, are movedarcuately around the disk. The periphery 342A may be knurled, ifdesired, to provide a good grip for the rubber roller.

Stud 335 serves as a support for a small electric coil 313, the core ofwhich is shown at 319. The core terminates in a tip 330 which is veryclose to, but spaced from the magnetizable ring 341. Whenever anelectrical signal is impressed upon the coil 316I the portion of thering 341 which is then under the tip 330 is magnetlzed. The member 36|also serves as a mounting for the magnifying glass 33| which is locatedover a window in member 36| so that the graduations 342B will be readilyvisible therethrough. The map 9 AN k nifying glass is provided with asighting line 332 ffltltsrnating' current for purposes of accuratereading. The coil 313 is energized through a lead wire 333 which extendsout of the side of the coil and through the arcuate slot 333.

At another part of the disk 342 there is mounted a'second coil generallydesignated 333. The coil 333 is identical with coil 313 and is lprovidedwith a core terminating in a\ tip 333 likewise located very close to butslightly spaced from the vmagnetizable ring 341. Coil 333 is mountedupon a V-slot and has a sidearm 331 against which an adjusting screw 333is adapted to bear. The adjusting screw is mounted in' the clip 339. Asthe screw 333 is turned the arm 331 is lifted or lowered and hence thecoil 333 may be moved either way along the line of the double arrow 393.A scale 391 is located alongside the coil so that its position relativeto the disk can be readily determined. The coil 333 is energized throughan incoming pair of lead wires 393 which aretaken out through the end ofthe arcuate slot 333. An erasing coil 394 is mounted solidly upon thefront of disk 342 and is provided with a core 395 extending close to butwith slight clearance from the magnetizable ring. The erasing coil whenenergized with direct curany magetized signals on the ring 341.

Figures 13-14.-The electrical circuits of thev station apparatus oareillustrated in Figures 13 and 14. When reading these diagrams theyshould be arranged with Figure 13 to the left and Figure 14 to theright. The apparatus of Figures -12 is schematically illustrated at theright end of Figure 14 which shows the synchronous motor 333 driving thedisk 343 upon which the neon lamp 349 is mounted. The fully adjustableor No. 1 pick-up coil 313 which is the movable one is likewise shownalong with the No. 2 pick-up coil' 333 that is stationary except forslight adjustments occasioned by rotating screw 333. The erasing coil isshown at 394 and the neon light circuit connection at D. The synchronousmotor is energized from alternating current lines L1 and La throughswitch 111, and the frequency meter 393 is connected across the lines.The frequency indication provides a basis for adjusting screw 333 andfor thus imposing a slight movement of coil 335. The pick-up coil 318 isconnected by means of its (shielded) cable 393 to station pre-amplifierNo. 1 which is completely shielded by grounded housing 391. The shieldof cable 333 is connected to this housing and the conductor to anotherportion, as later described. Similarly, pick-up coil 333 is connectedthrough its shielded conductor 393 to station pre-amplifier No. 2, theshielding of the cable being connected to grounded case 393 whichlikewise serves to shield the pre-amplier. The internal lead of vthecable 393 is connected to the pre-amplifier No. 2 as later described.

Referring to Figure 13, under the bracket generally designated 433 thereis villustrated what may be described as the thyratron chassis. In thisportion of the apparatus there is included two power supplies, two gastype trigger tubes (thyratron) and a plurality oi switches, preferablyof the microswitch type, that are manually operated, as hereinafterdescribed. Under the bracket 431 there is illustrated a power supply No.1T while over the bracket 432 there is illustrated an identical powersupply No. 2T. Since these power supplies are identical only one need bedescribed as representative.

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supply is provided over lineslaandhandswitchlwhichservesto energize theprimary winding 433 of the transformer generally designated 433 and alsothat of I power supply No. 2T. It may be noted incidentally that allalternating current service lines to the installationk maybe servedthrough this one switch, if desired. or separate controls may be used.The transformer 433 has a secondary 433 which serves through switch 123.to feed the iliamentcathode 431 oi' the full wave rectifier tube 433.The transformer also has a higher voltage secondary 439 which isconnected to the two anodes 413 and 41| of the full wave rectifier tube433. The positive output line 412 is connected to one side oi thetransformer winding 433 and the negative output line 413 is connectedthrough switch 121 to the center tap 413 of the winding 439. Choke coil413 and a pair of condensers 411 and 413, connected in the usual way,serve to smooth out the direct current 'output which is applied to apotentiometer resistor 419 having an intermediate ltapf423 grounded at421. The tap 422 is apprpximately 20 volts negative and the tap 423approximately 400 volts positive.

, Similarly. power supply No. 2T. shown over the bracket 432, providesapproximately 20 negative volts on negative output terminal 424, groundpotential at tap 423 and approximately 400 volts positive at outputterminal 423. A direct current voltmeter 421 having one terminalgrounded at 423 is arranged to be connected through switch '|14topositive output terminals 423 and 423 of the two power suppliea'in orderto read either of the output voltages. An intermediate voltage tap 433is provided on the potentiometer resistor 43| of power supply 432 and isconnected through switch 432 to junction 433 and thence through resistor434 to lead 433 which ellrtends to the eraser coil 394, Figure 14. Aground lead 433 is connected to condenser 431 and also extends to theeraser coil. By closing switch 432 for a short time, condenser 431 ischarged to the voltage of tap 433 on power supply 432. This potential isalso applied through resistor 434 and lead wires 433 and 433 to theeraser coil 394.

When the push-button switch 432 is opened, condenser 431 dischargesthrough the resistor and the eraser coil. and the magnetism of this coiltherefore subsides to nero value, in a time period determined by thetime constant'of this circuit. During erasing the disc 343 is rotatedand hence a gradually d magnetism is applied to the disc for the erasingoperations.

Microswitches.-At the right-hand portion of each of Figures 13 and 14there are shown a plurality of microswitches designated I-VI in Figure13 and VII-X in Figure 14. Each of these switches has two operativepositions. Switches I-VI are operated mechanically by means of camsthrough asingle cam-actuated shaft controlled by the operator through asuitable handle 113, Figure 15. There are three sets of operatingconditions for switches vI-VI, as shown by Figures 17, 18 and 19.Microswitches VII and VIII are operated by an alternating currentsolenoid actuator Va. which is in turn energized by microswitches V.Switches IX and X are operated through an alternating current solenoidactuator Vla controlled by microswitch VI. The circuits for the solenoidactuators are as follows:

Alternating current is supplied through lines L1l and Le (at the centerof Figure 13). Line Li is connected to feeder 433 which extends to junc-11 tion 438 and thence to the common terminal 445 of switch V, anotherextension being to the common terminal 44| of switch VI. When switch Vis in the position shown in Figure 13 (same in Figure 17), a circuit iscompleted to terminal 442, switch V, whence power is conducted by way ofline 443 to 'the winding of the solenoid actuator Va, the return circuitto line I c being by way of line 444. Thus, when switch V h in theposition shown in Figure 13, the coil of solenoid actuator Va isenergized and the microswitches VII and VIII are held in the positionshown ln Figure 14. Switches VII and VIII are located within the shield581 of pre-amplifier No. 1 and are thus isolated from extraneouselectrical disturbances from coil Va or anything else. When switch V ismoved against contact 445 the circuit to coil Va is broken andmicroswitches VII and VIII move to the opposite position from that shownin Figure 14. Similarly when microswitch VI is in the position shown inFigure 13 (same for Figure 17) a circuit is completed from line L1through junction 438 to terminal 44| and thence through microswitch VIto terminal 446 whence the circuit continues by way of line 448 to thecoil of solenoid actuator VIa, the circuit being completed to line La byway of line 444. Thus, energizing the solenoid actuator VIa holdsmicroswitches IX and X in the position shown in Figure 14. Whenmicroswitch VI is moved to the position so that its movable contactengages the dead contact 441, the circuit to coil Vla is de-energizedand the microswitches IX and X move to the position opposite to thatshown in Figure 14, see Figure 18, for example.

There are three sets of operating conditions which are shown in Figures17, 18 and 19, these three conditions being the reading conditions forthe instrument marked Read," Figure 17, the condition under which thesignal from the range photocells are impressed upon the stationapparatus marked Range, Figure 18, and a testing condition under whichcertain tests of the instrument itself are made marked Disjuncture,Figure 19.

The signals from the muzzle and target range stations I8 and 22,respectively, are received by way of lines K and N (Figure 1) whichterminate at microswitches I and 1I, respectively, Figure 13. Incomingground lines G and G' of Figure 1 are not illustrated in Figures 13 and14. Thus, line K is connected to terminal 448 of microswitch I and whenthat switch is in the Range or Disiuncture positions, Figures 18 or 19,the circuit is completed to the common terminal 455 of the microswitchI, and thence through resistor 45| and condenser 452 to the primary 453of the transformer generally designated 454. The circuit is conmpletedto ground line 455 which is grounded at 456. The received signal fromthe range stations (either the muzzle or target stations) is a sharpnegative wave and this induces a similar sharp positive wave in thesecondary 451 of transformer 454. Secondary 451 is connected by line 458to the negative terminal 422 of power supply No. 1T which normallymaintains a negative voltage on the transformer secondary, and is alsoconnected directly to the grid 465 of a gas type trigger tube(preferably thyratron) generally designated 45|, Tube 46| is providedwith an indirectly heated cathode 452, grid 465 and anode 463. The anodeis connected by means of line'464 and condenser 465 to the ground line455 and is connected through line 461 and resistor 481 to the positivetermi- 12 nal 425 of power supply No. 1T. The transformer secondary 451is also connected through condenser 455 to the ground line 455 whichsupplies a high frequency pass for the sharp wave signal induced in thesecondary. Cathode 452 is connected through the primary 415 of thetransformer 41| to ground line 455. The trigger tube 45| is ordinarilynot conductive and the condenser 455 charges to the voltage of outputterminal 425 by means of the charge line 451 in which there is locatedthe resistor 451.

The grid 455 of the trigger tube is normally maintained negative throughtransformer secondary 451 and the connection 455 to the negativeterminal of the power supply. When the sharp negative signal wave isimpresed upon winding 455, this induces a positive signal at winding 451which momentarily shifts the grid 465 to the positive condition,whereupon tube 45| becomes conductive and remains conductive until thecharge on condenser 455 is dissipated, whereupon it ceases to conductsince there is no longer any appreciable voltage existing across thecondenser 465. Resistor 451 is of high enough value that it will notsupply current for continuing the discharge.

This momentary discharge surge is impressed upon the primary 415 of thetransformer 41| and induces a signal current surge in the secondary 413of that transformer through a circuit extending from ground 456, throughground line 455, thence to terminal 414 through the secondary 415, line415, terminal 416 to theanode 411 of the full wave rectifier tube 418,thence to the cathode 418 of the rectier tube and to the terminal 455 ofthe cathode heater supply transformer. The circuit continues throughresistor 45| and line D to the neon tube 548 on the revolving disc andthence to ground. Thus, an incoming signal from the photocell at themuzzle range station I8 produces a momentary flashing of the neon lighton the rotating disk 845, To junction 415 (see Figure 13 neartransformer 41|) there is connected a resistor 453 which is connected tothe ground line 455 at junction 484. The cathode of the full waverectifier tube 415 is powered by secondary winding 485 of transformergenerally designated 455. The primary 481 of the transformer isconnected to alternating current feeders 458 and 444.

In an analogous manner, a signal received on line N from the photocellstation located at the target range station 22 is applied to terminal485 of the microswitch II. When the microswitch is in the "Rangeposition, Figure 18, the signal is communicated to microswitch terminal485, whence the circuit continues through resistor 45| and condenser 482to the primary 455 of a transformer generally designated 454, and thenceto ground line 455. One terminal of the secondary 485 of the transformeris connected by line 485 to the negative terminal 424 oi' power supplyNo. 2T shown over the bracket 452 and is likewise connected throughcondenser 481 to the ground line 455. The opposite terminal of thesecondary 485 is connected directly to the grid 455 of the gas-filledtrigger tube 488. This trigger tube is identical with that illustratedat 45| and includes an indirectly heater cathode 555, grid 485 and anode55|. The anode is connected through line 552 and resistor 558 to thepositive terminal 425 of power supply No. 2T and is connected throughcondenser 555 to the ground line 455. The cathode 555 is connectedthrough the primary 555 of the transformer 551 to the ground line 455.The secondary 555 of transformer 551 is grounded at 13 Junction v414,the opposite terminal being connected through line 555 and junction |5to the anode 5|2 of full wave rectiilertube 413. A resistor 5|3 isconnected between junction 5|5 a'nd Junction 454 on the ground terminal,

Thus, when a signal is received from the target range station 22, thesharp, negative wave received on line N is communicated through themicroswitch II to the transformer primary 453 which serves to induce asimilar sharp positive wave in the transformer secondary` 455, thusswinging the normally negative grid 493 of the trigger tube 459 to thepositive condition causing that tube to become conductive. -This causesthe charge on condenser 555 to be dissipated through '14 The anode 552of the pcntode tube 545 is connected by line 533 through Junction 554,condenser 535 and resistor 555 to the ground line.

the primary 555 of the transformer 551. thereby light being grounded atthe disk.

In Figure i4 the upper and lower parts of the diagram include twoamplifiers, ampliiler No. 1

under the bracket 5|5 and amplifier No. 2 over the bracket 5|5. Each ofthese ampliiiers includes a pre-amplifier section, namely pre-ampli-!ier No. '1 and pre-ampliiler No. 2. The preamplitlers are housed ingrounded, shielded cases shown by the dotted line outline 391 and 395previoly referred to..

Referring to ampliner No. 1, a power pack, not illustrated, is connectedacross'the potentiometer resistor 5|1l through switch 135. The resistorhas a ground at 5|5 and has a negative terminal 519 of about 110 voltsnegative, a 12S-volt positive tap at 525, a 180-volt positive tap at 52|and a 240- volt positive tap at 522 which is the positive outputterminal. A bridging resistor 523 is con- `nected across the ground andnegative terminals and is provided with an intermediate voltage tap 524.I

The input to the pre-amplifier section of ampliiler No. l is by way ofthe shielded cable 333 which is connected to the terminals 525 and 525of microswitchesVII and VIII, respectively. Contacts 521 and 525 ofthese microswitches are grounded. Movable contact 525 of microswitch VIHis connected via line 535 to the movable contact 532 of microswitch III.The movable contact 535 of microswitch VII is connected to one terminalof the primary winding 534 o! the transformer 535, the other terminal ofthat winding being connected to ground line 545. The secondary winding531 is connected to the ground line 545, and the opposite terminal isconnected through junction 54|, inductance 542 and junction 543 to thecontrol grid 545 of the pentode amplifier tube generally designated 545.

Tube 545 includes a cathode 541 which is connected through junction 545to the suppressor grid 549 and from junction 548 there is a parallelcircuit composed of resistor 555 and condenser 55| extending to theground line 545. A pair of condensers 552 and 553 are connected fromjunctions 543 and 54 I, respectively, to the ground line 545. The grid554 is connected through condensers 555 and 555 in parallel to theground line 545 and'is connected by way of junction 559 and throughresistor 559, junction 555 and line 55| to the positive terminal 522 ofthe power supply.

vpositive terminal 522 on the power supply.

The four-element amplifier tube generally des- :ensued m includes anindirectly heated cathode 515. a control grid 51|, second grid 512 andanode 513. The cathode 515 is connected through iunction 514 and throughresistor 515 and condenser 515, in parallel. to the ground line 545. Thegrid 512 is connected through line 511 to tap 525 of the power supply.Anode 513 is connected to Junction 519 and thence through resistor 555to tap 52| on the power supply. 'I'he grid 51| is connected to avariable tap 55| on resistor 555 by which the gain of this tube may bevaried. Prom 519 a circuit extends through condenser 532 kto Junction583 and thence through resistor 554 to variable tap 524 on resistor 523.The variable tap 524 regulates the bias of tube 555.

' Tube 555 is a. gas-illlcd trigger tube of the thyratron type andincludes an indirectly heated cathode 555, control grid 551 and anode555. The grid 551 is connected through resistor 559 to junction 553 andcathode 555 is connected through line 595 directly to ground line 545.The

anode is connected to Junction 59| whence a circuit extends throughresistor 592 to tap 52| on lthe power supply. From junction 59| acircuit also extends through 'condenser 593 and resistor 554 to groundline 545. From tap 595 a circuit extends to contact 595 of push buttoncontrolled microswitch B. The microswitch B also includes a contact 591which is connected by way of line 555 to junction 599. 'I'he movablecontact 555 of the push button controlled microswitch B is connected byline 55| to contact 552 of cam controlled microswitch I.

From junction 59| a testing circuit extends via line 553 throughnormally open switch 554 and thence through resistor 555 and neon light555, in parallel, and through condenser 551 to ground line 555.

Amplifier No. 2 shown over bracket 515 is of precisely the same type asamplier No. 1. The input to the preamplifier portion of amplifier No. 2is byway of shielded cable 993 which is connected to contacts 559 and5||| oi microswitches IX and X, respectively. Contacts 5|| and 512 ofthese microswitches, respectively, are grounded. Movable contact 5|4 ofmicroswitch IX is connected by means of line 5|5 to movable contact 5|1oi microswitch IV, Figure 13. Contacts 515 of microswitch III and 5|9-of microswitch IV are connected together and grounded at 525. Contacts52| of microswitch III and 522 of microswitch IV are likewise connectedtogether and to line D at Junction 523.

'Ihe movable contact 525 of microswitch X is connected to the primary525 of transformer 521. The primary 525 is connected to ground line 525.The secondary winding 590 of the transformer and condenser 53| areconnected .in parallel at junction 532 and are connected to ground line523. From junction 532 the circuit extends through inductance 533 andthence to the grid 15 Y denser 642, in parallel, to ground line 626. Froanode 643 a circuit extends over line B44 to Junction 046 and thencethrough condenser 646 and resistor 441 to ground line 626. From junction64I a circuit extends through resistor 649 to junction 660 and thenceover line 66| to the positive terminal |62 of the potentiometer resistor663. The potentiometer resistor is supplied through switch 134 from'anindependent powerpack of the type described with reierence to amplifierNo. 1. llrom' grid 664 o! pentode 635 a circuit extends through Junction666 and 666 and through condenser 661 to the ground line 626. Acondenser 660 is connected between junction |66 and ground and sresistor 669 is connected between Junction 664 and 660, and thence overline 66| to positive terminal 862.

The tetrode amplifier generally designated 660 has an indirectly heatedcathode 66| which is connected through resistor 662 and condenser 663 inparallel to ground line 626. The control grid 664 of the tetrode, isconnected to the variable tap 665 of resistor 641 by which the gain ofthe tetrode amplifier is regulatable. The grid 666 is connected to tap661 on resistor 653, and the anode 668 is connected through junction 669and resistor 610, junction 61| to tap 612 on the resistor 653. Junction669 is connected through a condenser 613 to junction 614 from which acircuit extends through resistor 615 to variable tap 616 on the biasresistor 611. The bias resistor is connected to the ground tap 618 andto the negative terminal 619 of the potentiometer resistor 653, and byvarying the adjustment of the tap 616, the bias of the tetrode 660 maybe varied. From junction 614 a circuit extends through resistor 680 tothe grids 68| of the gas-lled trigger tube 682. The trigger tube has anindirectly heated cathode 683 connected to the ground line 628 and ananode 684 that is connected to junction 685. From junction 685 a circuitextends through resistor 681 to junction 61| and thence to tap 612 onthe potentiometer resistor. Likewise from junction 685 a circuitextendsthrough condenser 689 to junction 690 and thence over line 69| tojunction 599 from line 69| and continues to terminal 692 of microswitchII. From junction 690 a. circuit likewise extends through resistor 693to the ground line 628.

From junction 599 a circuit extends to terminal 694 of the push bottonoperated microswitch A. Microswitch A has a movable contact 695 which isnormally maintained in contact with the stationary contact 696 fromwhich a circuit extends through resistor 691 to tap 698 on thepotentiometer resistor 653.

The disjuncture charge circuit, shown over the bracket 100, consists ofa resistor and a condenser 102 connected in parallel between junctions103 and 104. Junction 103 of the parallel circuit is grounded andjunction 104 is connected to the movable contact 695 of the push buttonoperated microswitch A.

From junction 685, Figure 14 (the output of amplifier No. 2), a circuitextends over line 105, through normally open switch 106 and thencethrough resistor 101 and neon light 108, in parallel, and throughcondenser 109 to ground line 608. Both the neon lights 606 and 108,together with their parallel resistors and a control switch, are testingcircuits as indicated.

Figures 17, 18 and 19.- These gures show the position of the manuallyoperated microswitches I throughV'IandthesolenoidoperatedmicroswitchesVII through IX in the three operating conditions ofthe system, namely a"Read position (Pigure 17) when the` recorded signals are read, s Rangeposition during which the signals are received from the range andrecorded on the magnetic element of the revolving disk and a Disjunctureposition which is a circuit testing condition.

Figures 15 and 16.-The circuit apparatus Just described may be embodiedconveniently in a panel type mounting as shown in Figures 15 and 16.This mounting includes three main panels- 1I0,1|| and 1|2. Panel 1|| isprovided with a manually operable handle 1|3 which serves.A

through suitable cams not illustrated, to oporate the microswitches Ithrough VI. causing them to close the circuits as shown in Figures 13and 17, 18 and 19. The three operating positions Read Range andDisiuncture" are shown on the front of panel 1| Panel 1| I also includesthe double throw switch 1I4 and the meter 421 serving power suppliesNos. 1T and 2T.

Panel 1 i0 includes a voltmeter 1|6 which indicates the alternatingcurrent supply line voltage and a number of control switches 1|1, 1 |6,1|l, 120,12I, 122 and the push button 123. This panel also includes anumber of pilot lights 124, 126, 126, 121, 128 and 129. The purposes ofthese are ls follows: Switch 1|1 controls motor 336 and pilot light 124indicates when the circuit is in operation. Switch 122 is the generalalternating current control switch and pilot light 126 its indicator.Switch 1|8\ controls the plate circuit of tube 499 and switch 1|9 thefilament, These tubes require a long warm-up period. Pilots'126 indicateplate voltage and pilot 121 filament current of tube 499. Switches and12| control the 11iament and plate voltages of tube 46|, respectively:pilot light 128 indicates the filament current and pilot light 129indicates the plate voltage of said tube 46|.

Panel 1|2 includes a meter 130 (see Figure 14) which indicates thevoltage from ground to terminal 522 (power supply of amplifier No. 1)and from ground to terminal 662 (power supply of amplifier No. 2). Meter130 is connected through a double throw toggle switch 429, as shown inFigure 14, in order to read either voltage. This panel also includes atoggle switch 134 for turning ofI and on ampliiler No. 2, a toggleswitch 13| for turning off and on amplifier No. 1. Switches 135 and 134are not shown in Figure 14 as they control the alternating current feedto standard rectifier power packs (not illustrated) which in turn areconnected to potentiometer resistors 6|1 and 653. The energization ofampllner No. 1 and amplifier No. 2 is thus controlled by turning on or othe alternating current feed lines to the power packs feeding theseamplifiers. Pilot lights 132 and 13| are connected to the power suppliesof amplifiers No. 1 and No. 2, respectively, to show energization whenswitches 136 and 134 are closed.

At the bottom of panel 1|2 there is an adjustment knob 136 whichcontrols the "gain" regulatcontrols the gain regulating contact 56| ofamplifier No. 1 and a control knob 133 for varying contact 524 of thebias control of amplifier No. 1. Push button controlled microswitches Aand B that are used in the disjuncture test operation 75 are alsoincluded on panel 1|2.

of the appropriate control switches, the light sources |3 and 20 areilluminated and light falls upon the photocells |05 in each oi thephotocell and amplifierunits |0 and 22. When the ordnance piece |0'(Figure l) undergoing testing is nred. the projectile travels along theline |II| andv as it passes the line of sight --1I at the muzzle stationin the range, light from the light source I6 that has been i'alling'uponthe photocelland amplifier I8 is thus momentarily decreased in amount.As the projectile passes the line -13-14 at the target station the lightfrom light source 20 that hasbeen falling upon the photocell |05 in unit22 is likewise momentarily decreased in amount.. The photocells andtheir amplifiers operate upon decrease in light. The percentage decreaseis very small. Referring to Figure 8, under normal illumina tion thephotocell |05 has a steady current conducting effect and the potentialexisting between Junctions ||8 and |28 (lower left in Figure 8)` causesa steady. current ilow from junction |28 through line |29 and photocell,thence through line |36 and Junction |31, resistor |2|, junction |3| tojunction ||6 on ground line H8. When the photocell is illuminatedsteadily, amplifier tube |4| is conductive at a constant value. When thephotocell is darkened due to the passage of the projectile, the ampliertube |4| momentarily becomes less conductive. Under normal steady stateconditions curren-t flows from high voltage supply, i. e., contact 3 ofthe socket |04, through line |16, resistors and |13, junction |10, line|69, plate |46. cathode |42, line |54 to ground line ||8. The degree ofconductivity of the tube is determined by the 'negative bias on grid |43as determined by the bias cell |50. When the illumination falling on thephotocell momentarily decreases, the resistance of the cell increases,and there is accordingly a momentary negative voltage wave at junction|31 which is impressed through condenser |38 upon grid line |40 of -tube|4|. This causes the tube |4| to become less conductive (of greaterresistance) and hence the current flowing in its cathode-anode circuitdecreases. This produces `a momentary positive voltage wave at junction|10 in the plate circuit, and this is impressed through condenser |1|upon resistor |12 and is conducted through line |88 to grid |82 oftheamplifier tube |80.

Amplifier tube |80 which is normally conductive at a steady statebecomes more conductive due to the positive wave impressed upon itscontrol grid |82. The output circuit of tube |80 extends from terminal 3of socket |04, through line |16 to junction |11, then through line 2|5,junction 2|4, resistors 2|3 and 2||, line 206, to plate |86, cathode |8|and through resistor |93 to ground line |94. The momentary increase inconductivity of tube |80 (which is equivalent to a momentary decrease inresistance of the tube) has the effect of producing a negative voltagewave at `junction 201 in the plate circuit 206, and this is impressedthrough condenser 208 upon line 208 and through it to the control grid223 of amplifier tube 220.

Amplifier tube 220 is normally conductivev through-a circuit extendingfrom terminal 3 of socket |04 and through high voltage lines |16 and2|5, through resistors 238 and 234, line 23|, plate 224, cathode 22|,and resistor 223 to ground line |94. The momentary decrease in conduc-18 tivity o1' the tube 220l (which is equivalent to a momentary increasein resistance of Ithe tube) has the eii'ect of producing a positiveoutput wave 'at junction 232 in line 23| as the signal comes through.The output positive wave is impressed through condenser 240 upon line24| and thence to output terminal 5 of the plug |04A.

Before tracing through the energization o! signal inthe circuit shown inFigure 9, it may be pointed out that in ordnance testing Vthe wave shapeof the signal is equivalent to a relatively high frequency output andthat various low frequencies are objectionable. Despite many safeguardsagainst -the introduction of low frequencies from the commercial (60cycle) supply, some signals of this character are present in thecircuit. Likewise the muzzle flash of the ordnance piece undergoingtesting and explosion ash where an explosive projectile is tested,produces light signals which to some degree ilnd their wayA into thephotoelectric apparatus, and these likewise produce signals"of lowerfrequencies. In order to discriminate against these signals and to favorthe desired relatively higher frequency signals, condenser 208 (betweentubes and 220) is of small capacity. This condenser with resistor 2|0may be -considered as a high pass filter which discriminates against thelower frequencies. Thus, even in the ampliiler shown in Figure 8 whichis mounted directly below the photocell in the physical apparatus(Figures 5 and 6) provision is -made for discriminating against furthertransmission of the undesirable lower frequencies.

The positive output signal wave on terminal 5 I is communicated throughthe plug |04`|04A to line 280 of Figure 9 and thence through resistor292 and normally closed switch 293 to the con-trol grid 281 of thegas-filled trigger tube 204. The grid 281 of tube 284 is connectedthrough resistor 322 t-o the housing ground line 282. The resistor 324which is connected to the grid lead at 29| -and to tap 325 of the powersupply normally maintains Ithe grid 281 negative through resistor 292.The variable tap 325 is adjusted so as normally to maintain the grid 281negative by an amount slightly less than the incoming positive signalwave on line 290 and hence when the signal is received the grid 281momentarily swings positive and tube 284 ilres through a circuitextending from positive Itap 216 on the power supply potentiometerresistor 269, thence through resistor 304, junction 305, anode 288,cathode 285, resistor 296 to ground line 282. Tube 284 which thusbecomes momentarily of very low resistance serves to discharge condenser308 through a circuit extending from ground line 282, resistor 3|0,condenser 308, line 301, junction 305, through the anode-cathode circuitof tube 284, resistor 296 to ground line 282. very short duration occursat output terminal 309 and is communicated through line 3|3 to outputterminal 3 4 on the plug 3 5.

While tube 284 is non-conductive prior -to firing. no current ilowsthrough its anode-cathode circuit, and hence there is practically nopotential drop across resistor 296 in its cathode circuit, but

when the tube 284 becomes conductive and fires,

there is a relatively large potential drop -across resistor 296. Thishas the eifect of immediately stopping the ilring oi' the tube.

It may be pointed out also that most of the current flowing through thetube when it res is from condenser 308 due to the relatively high valueof resistor 304 and that when switch 283 is open, the tube will nreperiodically at a rate de- When this occurs a wave of 19 termined by thesize of condenser 333 and resistor 334. This serves as a convenientmeans of testing the operation of the gas tube apparatus since merely byopening switch 233 it is possible to impress upon the output 333 aseries oi repeated, sharp negative waves. Any deviation from this normaltesting response clearly indicates some erroneous operation of theapparatus. Likewise, when 'switch 293 is opened the input signal onterminal may be tested conveniently by connecting an oscilloscope to theoscilloscope jack 332. The spring terminal 333 of the jack is connectedthrough line 334 to the input signal terminal 5 of plug |34A, the otherterminal 335 of the jack being grounded. Thus, by connecting anoscilloscope to jack 332, it is possible to test the incoming signalreceived at the apparatus of Figure 9 which, in the physical embodiment,is in the base 82 of the stand.

At the station unit 25, Figure 1, the incoming signal from the muzzlephotocell and amplifier station i8 is received over line K, and thesignal from target station is received over line N. Since it is assumedthat the handle 1|3, Figure 15, has been moved to the Range position,microswitches I through VI are thereby manually positioned as shown inFigure 13 (same in Figure 18) and microswitches V and VI thereby controlmicroswitches VII through IX to the corresponding positions as shown inthese gures. The signal received upon line K (Figure 13, upper center)is thereby impressed through resistor 45| and condenser 452 upon thetransformer primary 453. The incoming signal is avery steep negativewave front and this induces a steep positive Wave front in the secondary451 of the transformer 454 causing the grid 463 of the gas-filledtrigger tube 46| to be swung momentarily positive. Tube 46| thereuponbecomes conductive and serves as a discharge path for the charge storedupon condenser 465 as previously explained. The sharp surge through thetube 46| passes through the primary 410 of transformer 41| therebyinducing a signal in secondary winding 413 which is transmitted throughrectifier tube 418, line D and the microswitches to the No. 1 pick-upcoil 318 adjacent the rotating disk 345 through a circuit as follows:From ground 456, Figure 13, a circuit extends through line 455, junction414, secondary winding 413, junction 416, through line 411 to cathode419 of tube 418, thence through junction 480, resistor 48|, line D tojunction 623. The line D from junction 623 extends to the neon light onthe revolving disk and hence the light is iiashed but this is incidentalto the recording of the signal on the disk 345 for the circuit branchesat 623 on line D and extends to contact 62| of microswitch III and tocontact 622 of microswitch IV. Since the movable contact 6|1 ofmicroswitch IV is in engagement with contact 6|9 (that is grounded at623), no circuit is completed from contact 622 of microswitch IV, but acircuit is completed from contact 62| of microswitch III, throughmovable contact 532 and thence over line 530 to movable contact 523 ofmicroswitch VIII which is then in the position to engage its contact 526from which the circuit continues over shielded cable 383 to No. 1pick-up coil 318, which now acts as a recording coil and produces amagnetic signal on ring 341 of disk 346. It may be noted that at thistime movable contact 536 of microswitch VII is in engagement with itsground contact 526 thereby preventing any leakage of the high frequencysignals across into the pre-amplier of amplifier No. 1 which `might.occasion erroneous operation of that am- As the projectile passes line13-14 at the target station it actuates the photocell and amplifier 22,Figure 1, thereby initiating a signal which comes into the station unit23' via the "target line N, Figure 13. Since microswitch II is inengagement with its contact 433, the sharp, negative wave signal isimpressed through resistor 43| and condenser 432 through the transformerprimary 433 to ground line 453. 'This induces a sharp positive wave insecondary 433 ot transformer 434, thus initiating the discharge throughthe gas-illled trigger tube 433, in exactly the same manner as for tube43|. The charge upon condenser 335 which had been built up throughresistor 333 during the time tube 433 was non-conductive, is therebydischarged through tube 433 and through the primary 333 of transformer531.l Consequently, a voltage is induced in secondary 533 which' isconducted through rectier tube 413 to junction 323 of the line D, whereit is distributed to the neon light 343 causing it to ilash and alsothrough microswitch III to No. 1 pick-up coil 313. This causes theenergization of the pick-up coil, which, acting again in its recordingcapacity, makes a second magnetic record on ring 341 of disk 343. Sincethe disk is rotated by the synchronous motor 333, the passage of theprojectile thus causes two magnetic records to be recorded on themagnetizable rings 341 of the disk 343 at angular spacings determined bythe speed of the disk and the speed of the projectile. The record may beplayed back by moving the operator handle 1|3 to the Read position.

Read position-With the handle 1|3 in the Read position, microswitchesI-VI are moved to the position shown in Figure 17 and in that positionthe switches V and VI actuate switches VII-X to the positions also shownin Figure 18. It will be recalled that both of the magnetic records onthe rotating disk 346 were impressed by means ot No. 1 pick-up coil 318.As the disk rotates, however, the magnetic records on the disk serve ateach revolution to induce slight electromotive forces in both of thepick-up coils 318 and 385. Whenever a voltage is thus generated in oneof these coils, it is ampliiled either through amplifier No. 1 orampliiler No. 2, depending upon the pick-up coil in which the voltage isgenerated. ASince the action is identical for both pick-up coils andampliner, only one need be described.

Assuming that the leading magnetic record passes under No. 1 pick-upcoil 313, the voltage thus generated is transmitted by way of shieldedcable 383 through microswitches VII to primary 534 of transformer 535which induces a voltage in secondary 531 that is applied to the grid oftube 546. The incoming signal from the pick-up coil is an approximatelysymmetrical wave, but tube 548 is biased so that the output in its platecircuit 563 is predominately negative, the positive portion of the wavebeing suppressed at least in part. The output oi tube 543 is transmittedthrough condenser 365 and resistor 533 to the grid 51| of tube 563. Thentube l563 is normally conductive but becomes less so when the negativesignal is applied to its grid 31| thus causing a positive signal atjunction 513 which is transmitted through condenser 332 to the grid 531of the gas-filled trigger tube 535. It may be pointed out that as in thephotocell amplifiers (Figure 8) condenser 332 serves to suppress the 21A lower frequencies and accordinglythe control voltage on the grid 581of the trigger tube is very sharp. The trigger tube 585 is normallynon-conductive but becomes conductive due to the incoming signal on itsgrid 581. The discharge through tube 585 is principally from thecondenser 593 since resistor 592 is of a sufficiently high valuey thatinsufficient current is passed to maintain discharge of the triggertube. Accordingly, as'the charge on condenser 583 is dissipated tube 585again assumes the non-conductive condition.` The discharge of condenser593 accordingly generates a very sharp negative voltage at junction 595which is conducted throughthe normally closed push buttoncontrolmicroswitch B and through microswitch I, resistor 45|, condenser -452and primary winding 453 of transformer 454 to ground. This induces asignal in the secondary 451 which eventuates in the operation of thenoon light 449 on the revolving disk 445 through an operation preciselythe same as when the incoming signal is received from the range, aspreviously-described. Thus, as the leading magnetic record passes underthe No. 1 pick-up coil, the neon light is caused to flash.

Similarly the trailing magnetic record passes under No. 1 pick-up coiland likewise causes the neon light to flash but since the disk has nowproceeded around through an angularity equal to the angularity betweenthe magnetic records on the disk, the neon light flashes occur inangularly disposed relationship. It will be assumed that the adjustmentof knob 315 is such that No. 1 pick-up coil is located at an angle inrespect to the No. 2 pick-up coil which is greater than the anglebetween the magnetic records on the disk 341. When this is true, thetrailing magnetic record approaches the No. 1 pick-up coil and causesthe second signal flash before the leading magnetic record passes underthe No. 2 pick-up coil. A third flash occurs when the leading magneticrecord passes under No. 2 pick-up coil, and the third flash occurs at anangle from the second flash which is equal to the difference between theangle between the pickup coils and the angle between the magneticflashes. Thereafter, as the trailing magnetic record passes under theNo. 2 coil, a fourth flash occurs. By rotating the knob 315` so as todecrease the angle between the pick-up coils, the two middle flashes(second and third) are brought gradually together until they coincide.When this occurs the operator knows that the magnetic coils are set atthe same angle as the magnetic records on the rotating disk and bysimply reading the angularity on scale 342B and knowing the rotary speedof the magnetic disk, it is possible to calculate the time elapsedbetween the flashes. Usually, the scale 342 is calibrated directly infeet per second for convenience.

The recording and reading presupposes a constant frequency impressedupon the driving motor 335. In order to provide for correction if thefrequency varies, there is provided a frequency meter 396 and theadjustment screw .388 which serves to move magnetic coil 385 angularlyin the direction of the double arrow 390. In the event of frequencydecrease this is equivalent to a decrease in the rotary speed of thedisk 346 and therefore for decreased frequencies there will be a smallerangle between the mag: netic records on the disk 340 than for higherfrequencies on the driving motor. By calibrating tnescale m .adjacentcon m in terms of' motor 338, but usually qfdinary ggod commen .cialservice sumces.

Thus, it win be observed that the .two anzu-- larly spaced magneticrecords in passing under each pick-up coil cause a pair of flashes ofthe neon light 3,49 and that the two pairs of flashes may be moved withrespect to eachother until the adjacent flashes off-the two pairscoincide. When this condition exists the angular spacing of the pick-upcoils is the same asthe angular l smcing of the magnetic records.

Disfuncture.-The Disjuncture condition is essentially an apparatustesting arrangement by which errors may be eliminated. When a magneticrecord passes under a pick-up coil, the nach is caused to occur in theneon light, as previously explained, but there is no way of tellingwhether the flash occurs when the pick-up of the magnetic record isunder the center of the coil or whether it occurs 'when the record isdisplaced one way or the other from the center line of the coll. Thereare unavoidable physical variations between the two pick-up coils 318and 385 and other variation -factors occur which are due to changes intemperature and operating conditions of thc various circuits andthermionic tubes. The Disjuncture circuit condition is provided as atest whether the magnetic records are in fact under the ,coils when theflashes occur. To carry out this operation the handle 1|3, Figure 15, ismoved to the Disjuncture position which causes switches I-VI to be movedinto the position shown in Figure 19 and switches VII-X are thenmagnetically actuated to the positions as also shown ir. Figure 19.Referring to Figure 13 it will be noted that when the movable contact ofmicroswitch A is normally in contact with contact 555. a positivepotential is impressed on contact 595 through resistance 691. Thisvoltage is communicated through movable contact 695 of switch A tojunction 104 and thence through resistor 15|A and condenser 102, inparallel, to ground terminal 103. This serves to charge condenser 102 toa.

| by way of microswitch B which is held in the l depressed conditionduring this operation. Therefore, the primaries 453 and 493 oftransformers 454 and 494, respectively, are simultaneously energized,tubes 45| and 499 simultaneously become conductive and the doublestrength signal is transferred through the recti- 4 fier tube 418 fromboth anodes at the same time to junction 523 on the line D. The neonlight 345 is flashed but this is incidental for the signal is alsotransferred by way of microswitch III and IV to both lines 530 and SI5simultaneously and thence by way of microswitches VIII and IX, re-

spectively, to the No. 1 pick-up coll 318 and No. 2 pick-up coil 385 soas to energize both of the coils simultaneously. Hence, there is placedupon the magnetic ring 341 revolving disk 345, two zones ofmagnetization which are angularly displaced by an angle equal to theangle between the No. 1 pick-up coil and the No. 2 pick-up coil.

The operator control handle H3 is then movedto the Read position and therecord is read. If everything is operating perfectly when such a recordis played back, the neon light will show three dashes. Actually, ifeverything is right there are two pairs otilashes but adjacent flashesof the two pairs coincide so that the signal actually appears as threeflashes of light angularly disposed, the two angles between adjacentflashes being equal to the angle between the two pick-up coils.

If the signal does not consist of three flashes, as above described, butinstead shows two pairs with the middle two close but visibly displaced,some malfunctioning exists. This can usually be corrected by varying thegain and bias of amplifiers No. 1 or No. 2 or both. By so doing theadjacent flashes of the two pairs can be brought into juxtaposition. Inthis -manner the instrument is adjusted so that the angular positionbetween the pick-up coils as read on the scale 342 will actually be theangular distance between the magnetic records on the revolving disk.

As many apparently widely different embodiments of this invention may bemade without departing from the spirit and scope thereof, it is to beunderstood that we do not limit ourselves t the specific embodimentsherein except as defined by the appended claims.

What we claim is:

1. A timing apparatus for recording and indicating short time intervalscomprising a record and indicating means including a circular member ofmagnetizable material and a quick responsive signal lamp both mountedfor rotation in a circular path thereon, motor means for rotating therecord and indicating means at a constant rate, a pair ofelectromagnetic elements movable relative to each other located adjacentthe circular member in cooperative electromagnetic relationship, a pairof incoming signal carrying circuits, a pair of amplifier networks, onefor each electromagnetic element and switch means responsive in onecondition of operation to communicate incoming signals received oneither incoming signal circuit to one of the electromagnetic elements torecord on the magnetizable member signals received on either incomingsignal circuit and responsive in another condition of operation tocommunicate signals generated by either electromagnetic element throughits corresponding amplifler network to the quick responslve signal.

2. The apparatus of claim 1 further characterized in that in a thirdcondition of operation of said switch means a testing signal charge iscommunicated simultaneously to both electromagnetic elements.

3. The apparatus of claim 1 further characterized in that theelectromagnetic elements are movable relative to each other whilemaintained in cooperative relation to the magnetizable eloment.

4. The apparatus of claim 1 further characterized in that each amplifiernetwork includes a thermionic amplifier tube and a gas-type trigger tuberesponsive thereto.

5. The apparatus of claim 1 further characterized in that each of saidamplifier networks includes an extremely sensitive shielded section andsaid switch means is located partly in each shielded section and partlywithout, the switch means part without the shielded section beingmanually operable and the switch means part within the shielded sectionbeing magnetically operated responsive to the operation of the switchmeans part without said section.

HARRY WILLIAM HOFFMAN. GROVER H. HELMER.

REFERENCES CITED The following references are of record in the le ofthis patent:

UNITED STATES PATENTS Number Name Date 1,365,470 Egerton Jan. 11, 19211,883,907 Hathaway Oct. 25, 1932 1,925,483 Dubois Sept. 5, 19332,011,366 Lord Aug. 13, 1935 2,012,170 Kayatt Aug. 20, 1935 2,091,357Goldsmith Aug. 31, 1937 2,213,534 Rowe Sept. 3, 1940 2,229,451 GulliksenJan. 21, 1941 2,245,124 Bonn June 10, 1941 2,298,608 Bates Oct. 13, 19422,336,897 Shipton Dec. 14, 1943 2,370,133 Begun Feb. 27, 1945 2,370,134Begun Feb. 27, 1945 2,370,166 Hoeven Feb. 27, 1945 2,370,176 Kornel Feb.27, 1945 2,395,127 Kornei Feb. 19, 1946 FOREIGN PATENTS Number CountryDate 317,477 Great Britain July 30, 1929

